Background

Blades are getting longer and slenderer, and therefore more flexible in torsion (twist).
Blades as the shown Siemens B55 are aeroelastically tailored to twist when they bend. This twist reduces aerodynamic forces when a wind gust hits the blade.
The structural integrity of such blades is dependent on this load mitigation – getting the twist coupling wrong will cause blade failure.
Validations of the blade torsion stiffness in the test stand and the bend-twist coupling in the prototype field test require accurate methods for blade bending and twist measurements.

Existing Solutions

All current methods for measuring bending and twist of blades in operation on a turbine are based on image processing of pictures taken of different types of targets on the blades:
- Siemens developed their own method shown to the right.
- Boulder Imaging use similar method with different targets claiming a position accuracy of 1.12 mm on a 50 m photo range.
- Berlin Wind use complex image processing of markings painted on the blade (no official documentation).
- Qualisys is general purpose motion tracking solutions, not used on wind turbine blades as far known to the applicants.
The image processing is done offline after the campaign of taking the pictures.
Sampling rate is typically below 5 Hz due to need for high resolution.
High data storage required.

Technology Overview

The two active targets, such as Infra-Red (IR) light sources, are mounted in a blade section emitting frequency-modulated light. The modulation ensures that they can be distinguished from each other and ambient light ().
The light sources can be either battery powered or connected to a self-generating power source.
A Position Sensitive Device (PSD) is used instead of a camera, tracking the positions of these light sources, whereby no image processing is needed; deflections and twist can be computed instantly in real-time with the same sampling rates as turbine load measurements (30 – 50 Hz).
A Proof of Concept project at SDU during 2020 has shown that the measurement method works indoor over a 10-meter distance.
The output of the system are directly timed series of deflections and twist, thus the requirement for data storage is minimal and validations of the measurement is instant.
The expected resolution of this system is about 1 mm for a blade length of 100 meter and scales accordingly with blade length.
The system can be extended with extra light sources along the blade span to measure the spanwise distributions of deflection and twist during blade operation.

Benefits

The technology has several benefits over existing technologies:

It is easier to install than existing technologies
It can provide measurements in several sections of the wind turbine blade
It requires less data handling capacity
It provides higher frequency and accuracy than existing technologies
Data can be evaluated near real time

Applications

Building into new wind turbines for constant monitoring
Test setups for new prototypes

Opportunity

Prior art exist for technologies that can measure torsion (twist) and bending of wind turbine blades. However, none of these utilize the frequency modulation that makes this version resilient towards other ambient light sources such as the sun.

Thus, a patent application focusing on different ways of implementing this feature in a functional and practical manner () has been submitted for PCT phase with the EPO as of October 2020. Patent application no: PCT/EP2020/077859.

The patent was updated with latest research data from our internally funded Proof-of-Concept (PoC) project where a prototype was built in 1:10 scale. This PoC brought us to TRL 4 and the results were added to the PCT application and included extensive insights regarding:

How to avoid noise from other light sources such as the sun
How to choose optimal frequencies for modulation
More qualified description on the type and placement of the light sources and cameras

The application was also updated based on input from industry regarding the market relevance for the product.

Based on the results of the PoC project and the confirmation obtained from industry parties, it is evident that a product based on the elements of this patent application is relevant and that it would make sense to develop it to a TRL closer to market so that it can be applied in industry. Note that from the IP we have examined in the process of writing the patent application, nothing have emerged that will prevent our freedom to operate for a product based on this technology.

Blade Motion Tracker

Patents

IP Status

Seeking